#include <iostream>
#include <algorithm>
using namespace std;

int id[210], gap[210];

bool cmp(int x, int y)
{
    return x > y;
}

int main()
{
    int m, s, c;
    cin >> m >> s >> c;
    for (int i = 1; i <= c; i++)
    {
        cin >> id[i];
    }
    sort(id+1,id+c+1);

    // 计算间隔，共c-1个间隔
    for (int i = 1; i <= c - 1; i++)
    {
        gap[i] = id[i+1] - id[i] - 1; // 两头都不空，所以要 - 1
    }
    sort(gap+1,gap+(c-1)+1,cmp);

    int len = id[c] - id[1] + 1; // 两头都要覆盖，所以要 + 1
    for (int i = 1; i <= m - 1; i++) // 减去间隔
    {
        len -= gap[i];
    }
    cout << len << endl;
    return 0;
}

#include <bits/stdc++.h>
using namespace std;

int id[210], gap[210];

bool cmp(int x, int y)
{
    return x > y;
}

int main()
{
    int m, s, c;
    cin >> m >> s >> c;
    for (int i = 1; i <= c; i++)
    {
        cin >> id[i];
    }
    sort(id+1,id+c+1);
    for (int i = 1; i <= c - 1; i++)
    {
        gap[i] = id[i+1] - id[i] - 1;
    }
    sort(gap+1,gap+(c-1)+1,cmp);

    int len = id[c] - id[1] + 1;
    for (int i = 1; i <= m - 1; i++) 
        len -= gap[i];
    }
    cout << len << endl;
    return 0;
}

对应：

1. 洛谷
2. 无名网 代码如下：

#include <iostream>
#include <algorithm>
#include<cstdio>
using namespace std;
int id[210], gap[210];
bool cmp(int x,int y)
{
  return x>y?true:false;
}
int main()
{
  int m,s,c;
  cin>>m>>s>>c;
  for(int i=1; i<=c; i=i+1)scanf("%d",&id[i]);
  sort(id+1,id+c+1);
  for(int i=1; i<c; i=i+1)gap[i]=id[i+1]-id[i]-1;
  sort(gap+1,gap+c,cmp);
  int l=id[c]-id[1]+1;
  for(int i=1; i<m; i=i+1)l=l-gap[i];
  cout<<l;
  return 0;
}